In a dynamic rigid disk storage device, a rotating disk is employed to store information. Rigid disk storage devices typically include a frame to provide attachment points and orientation for other components, and a spindle motor mounted to the frame for rotating the disk. A read/write head is formed on a “head slider” for writing and reading data to and from the disk surface. The head slider is supported and properly oriented in relationship to the disk by a head suspension that provides both the force and compliance necessary for proper head slider operation. As the disk in the storage device rotates beneath the head slider and head suspension, the air above the disk also rotates, thus creating an air bearing which acts with an aerodynamic design of the head slider to create a lift force on the head slider. The lift force is counteracted by a spring force of the head suspension, thus positioning the head slider at a desired height and alignment above the disk that is referred to as the “fly height.”
Head suspensions for rigid disk drives include a load beam and a flexure. The load beam includes a mounting region at its proximal end for mounting the head suspension to an actuator of the disk drive, a rigid region, and a spring region between the mounting region and the rigid region for providing a spring force to counteract the aerodynamic lift force generated on the head slider during the drive operation as described above. The flexure typically includes a gimbal region having a slider-mounting surface where the head slider is mounted. The gimbal region is resiliently moveable with respect to the remainder of the flexure in response to the aerodynamic forces generated by the air bearing. The gimbal region permits the head slider to move in pitch and roll directions and to follow disk surface fluctuations.
In one type of head suspension, the flexure is formed as a separate piece having a load beam-mounting region that is rigidly mounted to the distal end of the load beam using conventional methods such as spot welds. Head suspensions of this type typically include a load point dimple formed in either the load beam or the gimbal region of the flexure. The load point dimple transfers portions of the load generated by the spring region of the load beam to the flexure, provides clearance between the flexure and the load beam, and serves as a point about which the head slider can gimbal in pitch and roll directions to follow fluctuations in the disk surface.
The actuator arm is coupled to an electromechanical actuator that operates within a negative feedback, closed-loop servo system. The actuator moves the data head radially over the disk surface for track seek operations and holds the transducer directly over a track on the disk surface for track following operations.
The preferred method of attaching the head suspension to the actuator arm is swaging because of the speed and cleanliness of the swaging process. Swaging also provides a strong joint that resists microslip. The swaging process has been in use in rigid disk drives since the late 1960s for attaching head-suspension assemblies to actuator arms.
FIG. 1 is an exploded, isometric view of a conventional head stack assembly 10 including a load beam 12, an actuator arm 32 and a discrete base plate 24 with a boss tower 28. The head suspension assembly 10 includes a load beam 12 with a flexure 16 to which a head slider 20 having a read/write element or head is to be mounted. The load beam 12 includes a mounting region 14 at a proximal end, a rigid region 22 adjacent to a distal end, and a spring region 18 between the mounting region 14 and rigid region 22. Spring region 18 is relatively resilient and provides a downward bias force at the distal tip of load beam 12 for holding the read/write head near a spinning disk in opposition to an upward force created by an air bearing over the disk. The flexure 16 is to allow pitch and roll motion of head slider 20 and read/write head as they move over the data tracks of the disk. The head suspension assembly 10 is typically coupled to the actuator via the actuator arm 32 that is attached to the mounting 14 region of load beam 12.
A swage type attachment is used to couple the mounting region 14 of the load beam 12 to the actuator arm 32. To swage load beam 12 to actuator arm 32, actuator arm 32 and mounting region 14 include apertures 34 and 26, respectively. The base plate 24 having a boss tower 28 with a swage hole 30 extending therethrough and, typically, a square flange 36 is welded or otherwise attached to a bottom face of mounting region 14 of load beam 12. Boss tower 28 is then inserted through actuator arm aperture 34. One or more swage balls are then forced through swage hole 30 in boss tower 28 causing boss tower 28 to expand in actuator arm aperture 34. This expansion creates a frictional attachment interface between outside surface 66 of boss tower 28 and interior surface 68 of actuator arm aperture 34. The load beam 12 typically includes one or more processing holes 38 useful for aligning the load beam 12 with the base plate 24 and/or actuator arm 32. The base plate 24 and/or actuator arm 32 may optionally include corresponding processing holes 38a, 38b to facilitate alignment.
The design of the swage joint has been reduced in size to keep up with the miniaturization of disk drives. As the industry pushes to decrease disk spacing and to increase aerial spacing, the thickness of the base plate 24 and actuator arm 32 are constantly being decreased. However, recent moves to disk-to-disk spacing of under two millimeters have presented a severe problem. Miniaturization of the swage plates is not satisfactory because the torque-out capability that the swaged system drops too low to be useful.
What is needed is an attachment system that reduces head stack thickness without compromising torque-out capabilities.